1. Field of the Invention
The present invention relates to a method for organizing a production line, for example, a method for organizing a production line capable of producing a plurality of types of vehicles by a single production line, and in particular, relates to a method for organizing a production line capable of providing efficient production by absorbing differences in manhour due to the type of vehicles and to a vehicle body assembly method and a vehicle body assembly line, capable of reducing the length of the single line and exhibiting a high productivity.
2. Background Art
A conventional design concept for organizing the flow production system of, for example, vehicles is disclosed in Japanese Unexamined Patent Application, First Publication No. Sho 61-21870, in which two assembly lines including a main line for integrating main parts and a sub-line for integrating subparts are constructed.
A production line design for producing a plurality of types of vehicle mixed on a single line is disclosed in Japanese Patent (Granted) Publication No.2920801. The concept of the above patent is known as a production line whose assembly speed is changed suitably for producing a plurality of vehicle types on a single line with a favorable production efficiency.
As described above, a plurality of types of vehicle bodies are usually assembled by two production lines. In most cases, these two lines include the main line for assembling the main components and a subsidiary line for supplying the components collectively to the main line after assembling the parts into the sub-assembled components.
For example, car bodies, conveyed to an assembly line after the coating process, are assembled while passing through the main line, which comprises an installation line, an underside assembly line and so on. In assembling the car body in the main line, the sub-assembled components, which are sub-assembled in the sub-assembly line connected to the main line, are supplied to the main line.
In conventional production lines, it is inevitably necessary to design the production line to be able to produce the type of vehicle having the largest number of parts, when taking various factors such as forms of production, equipment, specifications, and the number of parts into consideration. Thus, the length of the main line increases, which results in increasing the redundant manhours and unnecessary utility expenses, and increasing the production cost.
That is, in order to produce a plurality of types of vehicles having different numbers of parts on the same line, the manhours required for one particular type of vehicle differ from those for other vehicles. Accordingly, when a type of vehicle having a small number of parts is conveyed on the main line, some of the manpower available for another type of vehicle having a larger number of parts becomes redundant.
One of the purposes of the present invention is to provide a method of organizing a production line, capable of producing a plurality of types of vehicles efficiently while absorbing differences in manhour due to the vehicle type.
Recently, the production of vehicles has changed from large scale production of a few types of vehicles to the small scale production of multiple types of vehicles, it has been a general trend to produce multiple types of vehicles on the same production line in response to diversified consumer demands. Accordingly, there has been a tendency for the production lines to become longer.
That is, considering the assembly forms, equipment, specifications, and the number of parts or components to be assembled, each of which differs for each vehicle type, the length of a production line for producing multiple types of vehicles must be determined based on the type of vehicle using the largest number of parts. Therefore, the length of the production line for producing multiple types of vehicles inevitably becomes long, which results in increasing the supplementary facilities, substantially reducing the productivity, and increasing the costs.
Furthermore, since a variety of vehicles comprising different numbers of parts and components are assembled on the same line, the number of manhours varies according to the type of vehicle. When a type of vehicle having a small number of parts is conveyed, the operators required for assembling a type of vehicle comprising a larger number of parts become redundant, and the productivity is reduced. Consequently, this redundant labor causes a reduction of the productivity and an increase of the cost.